docs: def i18n_alternate_links():
      """Render the <link rel="alternate" hreflang />
  
      if page is in a I18nBlueprint
      """
      if (not request.endpoint or
              not current_app.url_map.is_endpoint_expecting(request.endpoint,
                                                            'lang_code')):
          return Markup('')
  
      try:
          LINK_PATTERN = (
              '<link rel="alternate" href="{url}" hreflang="{lang}" />')
          links = []
          current_lang = get_current_locale().language
  
          params = {}
          if request.args:
              params.update(request.args)
          if request.view_args:
              params.update(request.view_args)
  
          for lang in current_app.config['LANGUAGES']:
              if lang != current_lang:
                  url = url_for(request.endpoint, lang_code=lang, **params)
                  links.append(LINK_PATTERN.format(url=url, lang=lang))
          return Markup(''.join(links))
      except Exception:
          # Never fails
          return Markup('')